Wattle
and Daub

Ian
Pritchett

A timber framed building with wattle and daub infill, limewashed in the medieval manner

For many people the
wonderful irregularities of wattle and daub walls and the undulations
of a distorted roofline form part of the attraction of a medieval timber
framed building. The walls gain their character from the timber frame
which forms the load bearing structure of the building, leaving open areas
between that have to be infilled to keep the weather out. The type of
infilling varies according to the function and status of the building,
its location within the country and the locally available materials. It
is probably fair to assume that if a material was readily available and
could be adapted for use it would have been used as an infill to a timber
framed building at sometime, somewhere.

Wattle and daub is
one of the most common infills, easily recognisable by the appearance
of irregular and often bulging panels that are normally plastered and
painted. It is an arrangement of small timbers (wattle) that form a matrix
to support a mud-based daub. The timbers normally fall into two groups,
the primary timbers or staves, which are held fast within the frame and
the secondary timbers or withies which are nailed or tied to, or woven
around the staves. Arrangement and sizes of panels vary from area to area
as does the orientation of the staves. The daub was applied simultaneously
from both sides in 'cats' (damp, workable balls) pressed into and around
the wattle in order to form a homogeneous mass. As the daub dried it was
often keyed by scratching or 'pecking'. Once the daub had hardened, the
surface was dampened to receive a lime plaster covering. The surface plaster
was usually made of lime and sand or other aggregates reinforced with
animal hair or plant fibre. The plaster was finished flush, or in some
cases, it would continue across the panels and timbers alike. This would
allow less important timbers to be concealed and only principal members
to be shown. The plaster may be smooth trowelled, rough cast or even parged
(incised and/or built up with a pattern or design).

PERFORMANCE

The
durability of wattle and daub is illustrated by this wall, still standing
after fire burnt the roof off.

A wattle and daub panel in need of repair

The eroded surface of a daub panel revealing its hair and straw binder

Wattle and daub may
not be the most rigid material, but therein lies its strength. It is able
to accommodate even the most severe structural movement; it is usually
well sprung into the timber frame and offers support to weakening timbers
that other forms of infill might not. Wattle and daub is not lightweight
or flimsy. Its weight is not dissimilar to bricks, however its insulation
is better and from a security point of view it can be far more difficult
to break through than brick. Although wattle and daub is porous and moisture
is absorbed when it rains, moisture levels are kept low because the daub
acts like blotting paper to disperse the moisture and because of the high
rate of evaporation from its surface.

In moderate, sheltered
conditions and if well maintained, a wattle and daub panel should last
indefinitely. Examples of 700 years old are known to exist.

Traditional infill
panels in timber framed buildings can perform extremely well if properly
constructed and maintained. Although in some areas of the country it was
normal for infill panels to have protective plaster coatings which extended
over the timber frame, it has become fashionable to remove plaster to
expose timbers. This is likely to compromise the performance of the building
and accelerate the decay of the previously protected structure. It is
unreasonable to expect to have a timber frame exposed on both sides and
not have draughts and/or some water penetration whether the infill panel
is traditional or modern.

Where timber framing
was not plastered over it was normal practice to limewash it each spring.
Although this was partly for hygienic reasons (being slightly caustic,
fresh limewash acts as a mild biocide and disinfectant), it had the tremendous
benefit of filling minor cracks caused by seasonal movement. Medieval
buildings would have looked quite different from the more recent black
and white interpretation that we see so often today.

In some cases weatherboarding
or tile hanging may have been added over the infill panels, particularly
on exposed gables, to protect them from the weather. Removing the protective
covering can lead to the recurrence of old problems all over again. It
would he wise to learn from our forebear's experience and consider alterations
only after careful thought and for good reasons, not purely on aesthetic
grounds.

Decay is often caused
by the introduction of hard cement in new renders and repairs, and by
the use of modern impervious paints. This is because cement based renders
are brittle and often crack, especially at the junction with the timber
frame. When it rains, water runs down the face of the panels because both
the cement and the modern paints are impervious, soaking right into the
wall behind wherever a crack is found. Thus the daub will get wetter and
wetter over time, leading to the decay of the timber frame and wattles
as well as soggy, unstable daub. Only soft, porous and flexible finishes
such as haired lime plaster and lime wash should ever be applied to daub.

REPAIR CONSIDERATIONS

Through the passage
of time buildings may become neglected and some damage is inevitable.
Knowing whether a damaged panel should be repaired or replaced, even with
experience, requires careful consideration, weighing up many factors such
as age, importance, rarity, position and function within the building,
condition and cost.

Although cost has
deliberately been put at the end of this list it will, in many cases,
be the deciding factor. Age, importance and rarity can be difficult to
define without research, however, bear in mind that all elements of ancient
fabric are important and that the loss of any eats away at our heritage.

REPAIR TO WATTLES

Repair to daub can
normally be implemented, even in the most extreme cases, providing the
wattles are still in good condition or repairable. Whereas repair to a
panel where the wattles have been totally consumed by fungal decay or
insect attack can be very difficult even where much of the daub/plaster
survives. Deterioration may be found in the wattles if they have been
damp, particularly if they are not oak or contain sapwood, and hazel seems
to be particularly prone to decay by woodworm (common furniture beetle).
Wattle panels with insect attack may need some localised treatment, but
are often strong enough to carry the daub. Introducing additional support
can increase their strength. This can take the form of new staves or withies
or timber battens or stainless steel mesh fixed across weakened areas.
Each repair will be different, depending on the circumstances. In general
finding the right solution is a matter of ingenuity based on the defects
and conditions found.

Repair to a wattle
panel may not be too difficult if the daub has already fallen away. The
wattle behind does not need to be absolutely rigid, but should be strong
enough to carry the new daub. It may be necessary to hold the wattle firm
whilst applying the new daub.

Where daub is still
in place the repair of a wattle panel can be much more challenging. In
some cases it may be possible to re-support or re-fix loose daub by using
non-ferrous wire ties or screws and washers. In some cases it will be
necessary to hold a panel carefully in position, or even totally remove
it in one piece, while repairs are carried out to the timber frame, and
then put it back. In this case specialist advice is essential if a disaster
is to be avoided.

REPAIR TO DAUB

Some shrinkage is normal
even in the most successful of historic daubs, and gaps around the edge
of the panel are usually caused by a combination of shrinkage within the
daub and the timber frame seasoning. These gaps allow the panel to move,
so to keep it weathertight they should be filled. They can easily be filled
with daub or lime mortar. If problems are experienced with excessive shrinkage
it is either because there is too much suction in the existing daub, or
the repair mix is unsuitable, but it is always easier to control the shrinkage
of a whole panel with the same moisture content. When areas of daub have
failed or become detached, they can be repaired by applying new daub to
fill the missing areas (after careful preparation and pre-wetting).

Problems can sometimes
be overcome by additional wetting of the existing daub or by modifying
the repair mix. The ingredients used in an original daub mix were normally
used because they were locally available and cheap, they may not have
been ideal. Nevertheless the first recommendation for a compatible material
would always be to use the original material. Old daub salvaged from damaged
panels can be broken up and mixed with a little water to make it useable
again. It may be necessary to add additional material to bulk it out,
or modify its performance. However, the required performance of a repair
mix may be different from the requirement for a whole panel. A useful
tip is to mix one part daub with one part of a good coarse lime mortar
to achieve a better-behaved material.

NEW DAUB MIXES

Daub
is generally made up of a combination of ingredients shown in the table
below.

Binders

Aggregates

Reinforcement

Others

Clay

Earth

Straw

Dung

Lime

Sand

Hair

Blood

Chalk
Dust

Crushed
chalk

Flax

Urine

Limestone
dust

Crushed
stone

Hay
or grass

Dung

The
binder holds the mix together, the aggregates give it bulk and dimensional
stability, the reinforcement helps hold it all together, control shrinkage
and provide long term flexibility. Some locally available materials may
contain more than one of the aggregates and other ingredients. For example,
subsoil may contain clay, sand and earth. There is some debate over whether
dung was deliberately added to daub mixes. It is probably reasonable to
assume that the presence of dung in daub mixes was due to using old straw
from animal sheds (why use fresh straw when it is valuable for animal
bedding?) and using animals to do the hard work of treading the daub.

Historically,
daub was a cheap material and lime was relatively expensive, so it is
unlikely that lime was included in daub except under special circumstances.
It is far more likely that the expensive lime would have been reserved
for the plaster and limewash, where it would be necessary.

There
are probably as many daub mixes as there are daub buildings. Try experimenting
with locally available materials. Remember to only add enough water to
make the mix workable, not so much as to cause excessive shrinkage. Another
tip is to mix the ingredients (without hair or straw) in advance and leave
the mix to 'temper'. It can then be re-mixed when required and the reinforcement
added. This will allow any dry ingredients to soak up water and for the
whole mix to have an even moisture content.

REPAIR TO SURFACE PLASTER

Where
the surface plaster has failed but the daub behind is still sound it is
normally possible to repair the plaster. It may be that the whole topcoat
to the panel has failed or been removed in the past in which case it will
be necessary to replace the whole area. Detached plaster can sometimes
be re-secured to the daub behind by means of small stainless steel screws
and washers, or re-adhered to the daub surface with a lime mix.

If
you are faced with having to repair or replace areas of lime plaster and
carry out minor repairs to the daub behind, it may be sensible to consider
using lime plaster for the daub repairs as well as the plastering. This
is often a sensible approach since it means only having to deal with one
type of material and can minimise the shrinkage problems that may occur
with small daub repairs.

New
woven hazel ready for daubing

REPLACEMENT PANELS

If
a wattle and daub panel is beyond repair or missing altogether then a
replacement panel will be required. Before removing any panels of a listed
building consult your local conservation officer. Listed building consent
will normally be necessary and you may be required to carry out recording
of the existing panels before proceeding. Some buildings constructed
before the 18th century were decorated with wall paintings to brighten
the home. These important works of early art vary from simple patterns
of repeated motifs to fine works of art and trompe lloeil architectural
elements. Whenever considering the removal of a panel it is essential
to be aware that original wall paintings or patterns could be hidden beneath
the layers of limewash, plaster or panelling.

Before
deciding upon a design for your new panels it is necessary to understand
why the old ones have failed and to address these reasons. For example,
there is clearly no point in replacing a panel damaged by a leaking gutter
if the leak is still there. Wattle and daub is the natural choice for
a replacement panel. The evidence of the previous panel will normally
dictate the species and pattern of the wattles. Most properly constructed
and maintained wattle and daub panels will out-live their builder.

Combining
as it does our understanding of traditional performance and the needs
of old buildings, wattle and daub has proved itself over time. Properly
maintained, the infill panels not only keep the weather out but also create
an environment where the structural timber frame is not at risk. Not only
is wattle and daub the sound choice from a constructional viewpoint it
is also the most environmentally friendly approach. The materials are
renewable, from sustainable resources, and minimal energy is consumed
in their production.

John McCann, 'Brick Nogging in the Fifteenth and Sixteenth Centuries, with examples drawn mainly from Essex', Transactions of the Ancient Monuments
Society, Volume 31, 1987

It
is likely that repairs to infill panels will take place alongside repairs
to the structural timber frame, so see also: SPAB Technical Pamphlet
No 12, The Repair of Timber Frames and Roofs by James Boutwood

This
article is reproduced from The Building Conservation Directory, 2001

Author

IAN PRITCHETT is managing director of
IJP Building Conservation, the company he founded in 1986. He lectures
widely on building conservation issues including lime in particular,
and is currently revising the SPAB's technical pamphlet No 11, Panel Infillings to Timber-framed Buildings. In addition to repairing all kinds of historic
buildings, IJP supplies traditional and ecological building materials through a
subsidiary company, Old House Store Ltd.